1. Field of the Invention
The invention relates to an apparatus for optical checking or monitoring of the surface of rod-shaped smoking articles and/or filter rods for the tobacco industry comprising a conveying means transporting the rods perpendicularly to their longitudinal direction, a light source for irradiating the surface of a rod disposed in the test location, a row of photoelectric transducers which simultaneously scan a line-shaped surface region in the longitudinal direction of the rod and an arrangement controlled by the production cycle for the detection, made by comparison, of surface faults from the output signals of the photoelectric transducer dependent on the reflection capacity of the line-shaped region of the surface.
2. Description of the Prior Art
Below the problems occurring in the optical checking or monitoring of rod-shaped smoking articles and/or filter tips or rods will be explained with reference to the monitoring of cigarettes. However, similar problems also arise with cigars, cigarillos or filter rods or tips.
In the production of cigarettes very close tolerances must be kept to for various dimensions, in particular the diameter and the length, in order to ensure the desired product quality as constant and defined as possible.
Various constructional forms of optical inspection means which can be used in the tobacco industry are known from German Offenlegunsschrift No. 2,542,082, German Auslegungsschrift No. 2,332,813, German Auslegungsschrift 2,451,199, U.S. Pat. No. 4,093,866, U.S. Pat. No. 4,149,089 and U.S. Pat. No. 3,812,349.
Whereas with these inspection apparatuses only a random monitoring of individual smoking articles is possible with apparatuses of the type of the present invention for optical monitoring of the surface of rod-shaped smoking articles and/or filter rods for the tobacco industry, as described in German patent No. 3,030,140, even with the present-day high production speeds of the order of magnitude of about 6000 rods per minute all the surface faults can be detected, i.e. not only fluctuations in the dimensions but also holes or dirt spots on the surface of the cigarette paper, changes in the contour, folds, and fluctuations in the location or exact formation of an imprint or stamp.
For this purpose the known apparatus comprises a conveying means, generally a transport drum, transporting the rods perpendicularly to their longitudinal direction and located at a suitable point in the cigarette manufacturing plant, a light source for irradiating the surface of a rod located in the test location, a row of photoelectric transducers which simultaneously scan a line-shaped surface region in the longitudinal direction of the rod, a memory unit for the image points of a plurality of adjacent scanning lines and two-dimensional integrators for the two-dimensional signal processing which also takes account of the manufacturing duty cycle.
A similar apparatus is known from German Offenlegungsschrift No. 3,420,470 in which on a first conveying means a first test zone portion is provided and on a second conveying means a second test zone portion. On each test zone portion at least two optical test means are aligned at different angles to the conveying plane and illuminate and scan adjacent axis-parallel peripheral portions of the rods running through the particular test zone portion. Each optical test means consists of a light source illuminating the axis-parallel peripheral portion of the rods and an optoelectronic sensor having at least one row of optoelectrical detectors for detecting the light reflected at the article surface. The peripheral regions of the rods concealed on passage through the test zone portion face the optical test means on passage through the second test zone portion so that in contrast to the apparatus according to German patent No. 3,030,140 the entire surface of a rod can be scanned.
However, detailed investigations with such an inspection apparatus have shown that there is still room for improvement. In particular, the accuracy is not satisfactory in detecting surface errors at the aforementioned high production speeds which meanwhile may be up to 8000 rods per minute.